Method and apparatus for monitoring operation of percussion device

ABSTRACT

A method and an apparatus for monitoring the operation of a percussion device, which percussion device comprises a percussion piston and a pressure channel for supplying pressure medium to the percussion device for moving the percussion piston. The method and the apparatus measure pressure pulsation of the pressure medium acting in the pressure channel, which pressure pulsation is depicted as a pressure curve. From pressure pulsation are determined parameters depicting the operating state of the percussion device and the operating state of the percussion device is determined on the basis of the parameters. In addition, an arrangement for controlling the operation of the percussion device on the basis of the operating state of the percussion device.

TITLE OF THE INVENTION

1. Field of the Invention

The invention relates to a method for monitoring the operation of apercussion device, which percussion device comprises a percussion pistonand a pressure channel for supplying pressure medium to the percussiondevice for moving the percussion piston, and which method measurespressure pulsation of the pressure medium acting in the pressurechannel, which pressure pulsation is depicted as a pressure curve.

The invention also relates to an apparatus for monitoring the operationof a percussion device, which percussion device comprises a percussionpiston and a pressure channel for supplying pressure medium to thepercussion device for moving the percussion piston, and which apparatuscomprises a sensor, arranged in connection with the pressure channel,measuring pressure pulsation of the pressure medium acting in thepressure channel and depicting said pressure pulsation as a pressurecurve.

The invention further relates to an arrangement for adjusting theoperation of a percussion device, which percussion device comprises apercussion piston and a pressure channel for supplying pressure mediumto the percussion device for moving the percussion piston, and whicharrangement comprises a sensor, arranged in connection with the pressurechannel, measuring pressure pulsation of the pressure medium acting inthe pressure channel and depicting said pressure as a pressure curve.

2. Background of the Invention

When holes are drilled in a rock with a rock drill machine, the drillingconditions vary in different ways. Layers in the rock mass may vary inhardness, and therefore characteristics affecting the drilling should beadjusted according to drilling resistance. In the drilling, there aresimultaneously four different functions in use: rotating the drill in ahole to be drilled, breaking the rock by hitting a drill shank with thepercussion piston as well as drill feed and flushing, by which drillingwaste is removed from the drilled hole. When rock is broken by strikingthe drill shank with the percussion piston, impact energy of thepercussion piston is transmitted by means of drill rods, whichconventionally serve as extensions of the drill shank, to a drill bitwhich strikes on the rock making it break. The correct operation of thepercussion device thus contributes considerably to the good drillingresult. Percussion hammers, in which a tool driven by the percussiondevice is arranged to break the surface to be broken, do not employ toolrotation nor flushing. It is mainly the operation of the percussiondevice that affects the breakage result, if the effect of the toolcharacteristics is not taken into account. Essential variables forbreaking the rock include length of an impact pulse, amplitude of theimpact pulse, impact frequency and a suitable bit/rock contact. Inpractice, of these variables all others but the length of the impactpulse are adjustable ones.

However, it is very difficult to control the operation of the percussiondevice such that the best possible drilling or breakage result isachieved, because there has been no reliable solution for monitoring theoperation of the percussion device. It is difficult to monitor theoperation of the percussion device while the drill or the percussionhammer is running. Attempts have been made to measure the position ofthe percussion piston with laser-operated or inductive sensoringsolutions arranged in the percussion device. U.S. Pat. No. 4,699,223discloses use of an inductive sensor for measuring the position of apercussion piston. A problem with solutions based on sensors arranged ina percussion device is poor durability of sensors in the demandingconditions, in which the drills and the percussion hammers are used.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a novel solution formonitoring the operation of a percussion device.

The method of the invention is characterized by determining, frompressure pulsation, parameters depicting the operating state of apercussion device and determining the operating state of the percussiondevice on the basis of said parameters.

Further, the apparatus of the invention is characterized in that theapparatus further comprises an analyzing device which is arranged todetermine parameters depicting the operating state of the percussiondevice from pressure pulsation and to determine the operating state ofthe percussion device on the basis of said parameters.

Further, the arrangement of the invention is characterized in that thearrangement comprises an analyzing device that is arranged to determineparameters depicting the operating state of the percussion device frompressure pulsation and to determine the operating state of thepercussion device on the basis of said parameters and that thearrangement comprises a control unit that is arranged to control theoperation of the percussion device on the basis of the operating stateof the percussion device.

The basic idea of the invention is that for monitoring the operation ofthe percussion device, which comprises a percussion piston and apressure channel for supplying pressure medium to the percussion devicefor moving the percussion piston, pressure pulsation of the pressuremedium acting in the pressure channel is measured, which pressurepulsation is depicted as a pressure curve, and parameters depicting theoperating state of the percussion device are determined from thepressure curve, and the operating state of the percussion device isdetermined on the basis of said parameters. In the present document thepressure curve refers to pressure pulsation that is measured at asampling frequency that is substantially higher than the runningfrequency of the percussion device, whereby very fast pressurevariations can be registered. Pressure pulsation is mainly generated bya reciprocating movement of the percussion piston, an impact of thepercussion piston, a rebound of the percussion piston and hydrauliccontrol provided by a control valve of the percussion device. Accordingto a first embodiment of the invention the operating state of thepercussion device is depicted on the basis of at least one of thefollowing parameters: a position of the percussion piston in thepercussion device, a piston stroke of the percussion piston, impactvelocity of the percussion piston and rebound velocity of the percussionpiston. According to a second embodiment of the invention the operatingstate of the percussion device is controlled on the basis of theparameters depicting the operating state of the percussion device.According to a third embodiment of the invention the percussion deviceis arranged for use in a rock drill machine and an operating state ofthe percussion device is determined on the basis of the parametersdepicting the operating state of the rock drill machine.

The invention has an advantage that the operation of the percussiondevice can be monitored accurately and in real time, which furtherenables the adjustment of the operation of the percussion device on thebasis of information obtained on one or more previous impacts. Thepressure curve of the percussion device can be measured in a simplemanner and the measurement can be carried out in the vicinity of thepercussion device, or elsewhere, on a boom or base carrying thepercussion device, whereby it will not be necessary to arrange anyfault-prone sensors in the percussion device. Further, the pressurecurve measurement and interpretation make it possible to monitor thetrend of the percussion device state and to use it for monitoring thecondition of the percussion device.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

In the following the invention will be described in greater detail inconnection with the attached drawings, wherein

FIG. 1 is a schematic side view of a percussion device, partly cut open,to which the solution of the invention is applied;

FIG. 2 is a schematic view of a pressure curve of pressure medium actingin a pressure channel;

FIG. 3 is a first pressure curve of a percussion device measured on arock drill machine;

FIG. 4 is a second pressure curve of a percussion device measured on arock drill machine;

FIG. 5 is a third pressure curve of a percussion device measured on arock drill machine;

FIG. 6 shows interdependence of the maximum tensile stress of a stresswave reflecting from the rock to be drilled, feed force and a variablerepresenting the quality of feed; and

FIG. 7 shows interdependence of the maximum tensile stress of a stresswave reflecting from the rock to be drilled, feed force and a secondvariable representing the quality of feed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIG. 1 is a schematic side view of a percussion device 1, partly cutopen. The percussion device 1 comprises a frame 2 and a percussionpiston 3. The percussion device 1 can be one employed in a drill or apercussion hammer. The percussion device 1 is hydraulically operated,and hydraulic oil, bio-oil or water can be used as hydraulic or pressurefluid. FIG. 1 further shows a pump 4 needed for driving the percussiondevice 1, which pump 4 pumps pressure fluid through a pressure channel5, in the direction of arrow A, to the percussion device 1 in order tomove the percussion piston 3 to the right in FIG. 1, i.e. to perform astroke. During a reverse stroke of the percussion piston 3 the pressurefluid returns to a tank 7 through a return channel 6 in the direction ofarrow B. FIG. 1 also shows a control valve 19 used for controlling theoperation of the percussion device 1. The general structure andoperating principle of the percussion device in the rock drill machineor the percussion hammer are known per se to a person skilled in theart, so they need not be described in greater detail herein, and for thesake of clarity the structure of the percussion device 1 is only shownschematically in FIG. 1.

FIG. 1 further shows schematically a pressure sensor 8, which measuresthe pressure of the pressure fluid acting in the pressure channel 5 andwhich is arranged in connection with the pressure channel 5 of thepercussion device 1. The measurement result obtained is the pressurecurve 10 shown schematically in FIG. 2 and representing impact pressurepulsation or pressure pulse of the pressure medium acting in thepressure channel 5. The horizontal axis of FIG. 2 represents time andthe vertical axis represents pressure. A measuring signal, whichadvantageously is a voltage signal, for instance, of the pressure sensor8, corresponding to the pressure curve 10, is transmitted through a wire11 to an analyzing device 9, where variables describing the operatingstate of the percussion device 1 are determined from the measuringsignal corresponding to the pressure curve 10. Parameters depicting theoperating state of the percussion device 1 or correlating with theoperating state of a percussion device include the following parameters,for instance:

-   -   t₁₁ an impact moment, i.e. a moment when the percussion piston 3        strikes the drill shank of the rock drill or the tool of the        breaking device,    -   t₁₂ back-timing of the control valve 19 of the percussion device        1, when the reverse movement of the percussion piston 3 starts        decelerating,    -   t₁₃ a back dead centre of the percussion piston 3, when the        percussion piston 3 changes its direction of motion,    -   t₂₁ a next impact,    -   p₁ the minimum pressure of an impact cycle, i.e. the pressure in        the pressure channel 5 at the impact moment,    -   p₂ an impact pressure value at time instant t₁₂,    -   p₃ the maximum pressure of an impact cycle, i.e. the pressure in        the back dead centre.

For instance, the following auxiliary parameters depicting the operatingstate of the percussion device 1 can be determined from the aboveparameters:

-   -   dt₁=t₁₂−t₁₁ a variable that is in proportion to the reverse        velocity of the percussion piston 3 and to the distance the        percussion piston has travelled from the impact point. It is        possible to use the variable indirectly for determining the        impact point, i.e. the position of the percussion piston 3 at        the impact moment and also for identifying the rock type.    -   dt₃=t₂₁−t₁₃ a parameter relating to the impact velocity,    -   t_(tot)=t₂₁−t₁₁ the time of an impact period, i.e. the inverse        of running frequency f,    -   x=(p₂−p₁)/(p₃−p₁) a ratio relating to the piston stroke length,        which can be used for adjusting the impact point, for instance.

On the basis of the parameters depicting the operating state of thepercussion device 1 or the auxiliary parameters determined therefrom itis possible to determine the operating state of the percussion device 1.For instance, the operating state of the percussion device 1 can bedepicted by one or more of the following variables: position of thepercussion piston 3 in the percussion device 1, piston stroke length ofthe percussion piston 3, impact velocity, rebound velocity, runningfrequency of the percussion device 1, or statistical parametersobtainable of the same.

The parameters depicting the operating state of the percussion device 1or auxiliary parameters determined therefrom and thus the operatingstate of the percussion device 1 can be used for determining thedrilling conditions. The drilling conditions refer to a drilling state,which is affected by the rock to be drilled, drilling equipment used anddrilling parameters, such as impact power, feed force, rotating torqueand flushing pressure, the measurable variables directly proportional tothem being impact pressure, feed pressure, rotating pressure andflushing pressure.

Thanks to the solution the operation of the percussion device 1 can bemonitored accurately and in real time. This also enables the control ofthe operation of the percussion device 1 in real time on the basis ofthe parameters depicting the operating state of the percussion device 1and obtained from one or more previous impacts, and thus on the basis ofthe operating state of the percussion device 1. The pressure curve 10 ofthe percussion device 1 can be measured in a simple manner. It is notnecessary to arrange any fault-prone sensors in the percussion device 1,but the measurement can be carried out in the vicinity of the percussiondevice, or elsewhere, on a boom or base carrying the percussion device.The pressure curve 10 measurement and interpretation make it possible tomonitor the trend of the percussion device state and use it formonitoring the condition of the percussion device 1 and the whole rockdrill or percussion hammer, for instance, in situations where thepressure curve 10 changes as pre-charge of the rock drill or thepercussion hammer accumulator changes or as the accumulator diaphragmbreaks or in situations where the pressure curve 10 changes as the rockdrill shank wears.

FIG. 3 shows a percussion device pressure curve 12 measured from a rockdrill. The pressure curve 12 is measured in a situation where thedrilling conditions have remained substantially constant. FIG. 3 alsoshows a point that corresponds to the minimum pressure of the impactcycle, i.e. pressure p₁ in the pressure channel 5 at an impact moment, apoint corresponding to an impact pressure value p₂ at a time instant t₁₂and a point corresponding to the maximum pressure p₃ of the impactcycle, i.e. the pressure at the back dead centre. FIG. 4, in turn, showsa percussion device pressure curve 13 measured from a rock drill, whenit hits a void. In the situation of FIG. 4 the parameter dt₁corresponding to linear momentum of the percussion piston and theparameter x corresponding to the piston stroke length have increased,because feed resistance has decreased. When the parameters dt₁ and xrise to a sufficiently high level, it indicates that the rock drill hashit a void, as has happened in the case of FIG. 4. FIG. 5 shows yetanother percussion device pressure curve 14 measured from a rock drillin a situation, where transfer from underfeed to sufficient feed hastaken place by increasing the feed. The underfeed was detected on thebasis of the parameter x.

FIG. 6 shows the maximum tensile stress 15 of a stress wave reflectedfrom the rock to be drilled, feed force 16 and a parameter x indicatedby curve 17 as measured from a rock drill. On the basis of the parameterx it is possible to determine whether the impact energy is excessive inrelation to the feed pressure. When the feed is sufficient, the tensilestresses do not decrease substantially and the value of the parameter xstabilizes. The level of the tensile stress indicates the actual qualityof drilling. Because it is very difficult to measure the tensile stressduring the drilling, the same objective will be achieved by means theparameter x.

FIG. 7 shows the maximum tensile stress 15 of a stress wave reflectedfrom the rock to be drilled, feed force 16 and moving standard deviation18 of the impact frequency determined from the pressure curve of thepercussion device pressure fluid as measured from a rock drill. Itappears from FIG. 7 that, when the feed force is increased and when ithas reached a given value, a drilling situation is achieved whichcorresponds to sufficient feed and in which the tensile stresses willnot substantially decrease. This can also be detected by the fact thatthe moving standard deviation 18 value of the frequency stabilizes.

FIG. 1 also shows a control unit 20, which is arranged to control theoperating state of the percussion device 1 on the basis of thepercussion device operating state determined in the analyzing device 9.The operating state of the percussion device 1 is conveyed from theanalyzing device 9 to the control unit 20. Instead of being two separateunits, the analyzing device 9 and the control unit 20 can be integratedinto one device or unit. In FIG. 1, the control unit 20 is arranged tocontrol the operation of the pump 4, for instance, by changing therotating speed or cycle volume of the pump 4. Instead of or in additionto the pump 4 control, it is also possible to control the operation ofthe percussion device 1 in a variety of ways, for instance, bycontrolling the operation of the control valve 19. It is also possibleto control the operating state of the percussion device 1, for instance,by controlling the feed force as described in connection with FIGS. 6and 7.

The drawings and the relating description are only intended toillustrate the inventive idea. The details of the invention may varywithin the scope of the claims. Hence, the percussion device 1 can alsobe operated by compressed air, whereby air, and not pressure liquid, isused as pressure medium, and the pump 4 can be replaced by a compressorand return air can be discharged directly into ambient air. Further, itshould be noted that the pressure curve pulsation may vary, forinstance, due to various pressure losses as hydraulic tubing is changed.

1. A method for monitoring the operation of a percussion device, which percussion device comprises a percussion piston and a pressure channel for supplying pressure medium to the percussion device for moving the percussion piston, the method comprising measuring pressure pulsation of the pressure medium acting in the pressure channel, which pressure pulsation is depicted as a pressure curve, determining, from pressure pulsation, parameters depicting the operating state of the percussion device and determining the operating state of the percussion device on the basis of said parameters, wherein the operating state of the percussion device is depicted by at least one of the following variables: the position of the percussion piston in the percussion device, the stroke length of the percussion piston, the impact velocity of the percussion piston and the rebound velocity of the percussion piston.
 2. A method as claimed in claim 1, comprising determining auxiliary parameters on the basis of the parameters depicting the operating state of the percussion device and determining the operating state of the percussion device on the basis of said parameters and the auxiliary parameters determined therefrom.
 3. A method as claimed in claim 1, comprising controlling the operating state of the percussion device on the basis of the operating state or the parameters depicting the operating state of the percussion device.
 4. A method as claimed in claim 1, wherein the percussion device is arranged for use in a rock drill machine and the operating state of the rock drill machine is determined on the basis of the parameters depicting the operating state of the percussion device.
 5. An apparatus for monitoring the operation of a percussion device, the percussion device comprising a percussion piston and a pressure channel for supplying pressure medium to the percussion device for moving the percussion piston, the apparatus comprising a sensor arranged in connection with the pressure channel for measuring pressure pulsation of the pressure medium acting in the pressure channel and depicting said pressure as a pressure curve and an analyzing device, which is arranged to determine parameters depicting the operating state of the percussion device from the pressure pulsation and to determine the operating state of the percussion device on the basis of said parameters, wherein the operating state of the percussion device is depicted on the basis of at least one of the following variables: the position of the percussion piston in the percussion device, the stroke length of the percussion piston, the impact velocity of the percussion piston and the rebound velocity of the percussion piston.
 6. An apparatus as claimed in claim 5, wherein the analyzing device is arranged to determine auxiliary parameters on the basis of the parameters depicting the operating state of the percussion device and further to determine the operating state of the percussion device on the basis of the parameters depicting the operating state of the percussion device and the auxiliary parameters calculated therefrom.
 7. An apparatus as claimed in claim 5, wherein the operating state of the percussion device is arranged to be controllable according to the operating state of the percussion device or the parameters depicting the operating state.
 8. An apparatus as claimed in claim 5, wherein the percussion device is arranged for use in a rock drill and the operating state of the rock drill machine is arranged to be determined on the basis of the parameters depicting the operating state of the percussion device.
 9. An arrangement for controlling the operation of the percussion device, the percussion device comprising a percussion piston and a pressure channel for supplying pressure medium to the percussion device for moving the percussion piston, the arrangement comprising a sensor arranged in connection with the pressure channel for measuring pressure pulsation of the pressure medium acting in the pressure channel and depicting said pressure as a pressure curve, an analyzing device, which is arranged to determine parameters depicting the operating state of the percussion device from the pressure pulsation and to determine the operating state of the percussion device on the basis of said parameters, which operating state of the percussion device is depicted on the basis of at least one of the following variables: the position of the percussion piston in the percussion device, the stroke length of the percussion piston, the impact velocity of the percussion piston and the rebound velocity of the percussion piston and a control unit which is arranged to control the operation of the percussion device on the basis of the operating state of the percussion device. 